By “extra-low voltage” is understood a voltage generally considered as “safety voltage”, which enables an operator to handle without danger any electrical component at said voltage. Such a voltage is moreover generally adapted to the electrical components of an information processing system. Several domains are legally defined in France and in Europe (ELV, SELV, PELV, FELV) but all place extra-low voltages below the threshold of 120 V with direct current and below the threshold of 50 V with alternating current.
The voltage of an alternating current distributed by an electricity distribution network is in general of the order of 220/230 V, which thus represents a priori danger for an operator. On the other hand, it is generally considered that a voltage of 50 V or less does not represent danger in handling. Thus, in telecommunications applications, the transmission data processing systems are generally subjected to a voltage of around 48 V. In aviation, the on-board components are generally subjected to a direct voltage of around 28 V. Finally, a computer type information processing system is generally subjected to a direct voltage of around 12 V.
An information processing system is for example a series of computer servers interconnected in a local network, thus forming a HPC (High Performance Computing) computer. In this case, as in other sensitive applications (computer server, desktop or laptop micro-computer, telecommunications radiofrequency station, etc.), it is important that the operation of the electrical system is not disturbed by failures in the current power supply, whether it is micro-power cuts of the alternating current power supply network or failures in the direct current power supply devices themselves. Indeed, such failures, even when they only last several hundreds of milliseconds, can bring about computing errors, losses of data or very penalizing malfunctions of the HPC computer.
By way of example, micro-power cuts are quite frequent, since the administrator of the alternating current power supply network may, as the need arises, have to black out parts of the network. These have in general a duration equivalent to several periods of the alternating current: for alternating current of 50 Hertz, a micro-power cut of ten to twelve periods thus lasts between 200 and 250 milliseconds. Moreover, the restart up of a direct current power supply device following a micro-power cut can itself also take 100 to 200 milliseconds, which gives a micro-power cut, seen from the electrical system, which can last up to 450 milliseconds.
When an electrical system, particularly of HPC computer type, is supplied by several direct current power supply devices, it is well known to choose each of these devices so that it is capable of supplying alone the whole of the current consumed by the electrical system while providing an analogical assembly for balancing the supplies, which ensures at each instant that the supply devices all supply current in substantially equal quantity as long as they are all operating. An additional precautionary measure consists in providing a different alternating current power supply source for each power supply device.
Thus, in the event of failure of one of the direct current power supply devices, either due to a failure of its alternating current power supply source or due to its own failure, the other device(s) can take over without risking reaching their power supply saturation. However, this solution is not optimal in terms of ecological consumption of electrical resources since, in normal operation of the supply devices, each of them then operates at less than 50% of its maximum capacity and far from its optimal efficiency. However, the standards that are being developed today are more and more demanding in ecological consumption of resources and require that the power effectively developed by direct current power supply devices is best adjusted to the electrical systems that they supply to improve efficiencies.
A solution, known as “Cold Redundancy Technology”, was recently introduced within the framework of the IDF2009 (Intel Developer Forum 2009), which was held from the 22 to the 24 Sep. 2009 in San Francisco (USA). This solution consists for example, when the direct current power supply comprises two supply devices, in only soliciting one at an optimal efficiency level and only starting the other when the electrical system to be supplied passes to a higher consumption level at a predetermined threshold or when a failure occurs in the active power supply device. But it is not indicated how the transition is managed in the event of failure. Indeed, each direct current power supply device comprises a capacitor or series of capacitors, known as “hold up” capacitor bank, capable a priori of resisting a mains power cut of several tens of milliseconds, for example around 20 ms. But failures (particularly mains power cuts) of a power supply device often reach several hundreds of milliseconds as does a transition of one device to another. The “hold up” capacitor bank thus does not make it possible to ensure a transition without risk of damaging the electrical system supplied.
Moreover, this solution is like twin supply systems with transfer of supply by automatic commutation, by means of a commutation management module, such as may be proposed by firms such as Schneider Electric. But these systems, generally proposed for vital installations such as a stock of medical devices of a hospital, are not adapted for installations more sensitive to power cuts such as servers or computing centers.
There is also known, from patent applications published with numbers EP 0 402 833 and US 2001/0022472, a solution consisting in providing, further to a first main power supply device and a second reserve or replacement power supply device, a supplementary back up electrical energy storage device able to be discharged during the transition phase between the first and second power supply devices in case of failure of the first one.
Finally, patent application published with number US 2007/0152506 discloses a primary direct current power supply source converting the alternating current of a commercial power utility. Furthermore, it is indicated that in case of complete failure of the primary direct current power supply source, a supplementary back up electrical energy storage source based on fuel cells is called into action. Moreover, capacitors are provided at the output of the fuel cells, so as to be continuously charged and for bridging between the primary direct current power supply source and the fuel cells.
But these solutions given by documents EP 0 402 833, US 2001/0022472 and US 2007/0152506 lack of reliability, since the failure information which may involve the transition phase and the possible start up of the back up device comes from the failing power supply itself.
It may thus be desired to provide a direct current power supply system with several supply devices that is both efficient from an ecological point of view, in other words efficient in its electrical energy consumption supplied by the mains, and reliable when a failure occurs.